Solderable conductor composition and a method of soldering a lead to a lead pad

ABSTRACT

A solderable gold conductor composition is formed by dispersing gold and certain inorganic binders in an inert liquid vehicle composition which can be used to produce conductor patterns which patterns adhere to fired ceramic substrates and to which can be soldered leads of electronic components. Limited ranges in the composition of, and the amount of, the binder particularly the amount of copper oxide are effective to produce adhesion of the composition to fired substrates and in permitting copper leads of electronic devices to be soldered to pads of the gold composition using a lead-indium solder after the composition has been fired on a substrate. Strong solder joints are produced without the necessity for physically or chemically cleaning the pads prior to soldering. The binders comprise certain amounts of the crystalline materials, copper in the form of copper oxides CuO or Cu 2  O, cadmium in the form of CdO, lead in the form of PbF 2  and the balance being a glass which also contains lead and some cadmium.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.942,728 filed Sept. 15, 1978, which in turn was a continuation-in-partof application Ser. No. 861,226 filed Dec. 16, 1977 for SolderableConductor Composition, both of which have become abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to noble metal compositions for producingsolderable conductor patterns which are adherent to substrates.

2. Description of the Prior Art

Conductor compositions which are applied to and fired on ceramicsubstrates, or on ceramic substrates provided with a thick filmdielectric layer, usually comprise finely divided noble metal particlesand inorganic binder particles. Such compositions are commonly appliedto substrates as a "thick film", a dispersion of the inorganic materialsof the compositions in an inert liquid medium or vehicle. The metalliccomponent of the composition provides an electrical conductor having lowelectrical resistance while the inorganic binders, such as glass, bondsthe metal particles to the substrate.

The most relevant prior art known to Applicants is that found in U.S.Pat. No. 3,970,590 which issued on July 20, 1976. This patent disclosesgold conductor compositions which can by conventional thick filmtechniques produce conductor patterns and pads to which electroniccomponents can be bonded using conventional thermal compression bondingtechniques. The particular gold conductor compositions disclosed in thePatent 3,970,590 have excellent adherence to ceramic substrates and suchsubstrates coated with thick film dielectric layers composed, forexample, of mixtures of alumina and glass. However, the strength of thesolder bond, or joint between a pad made of the composition, a lead pad,and a copper lead precoated with solder varies from being unacceptablyweak to being acceptably strong.

The major problem with the prior art gold conductor composition is thatthe strength of solder joints between lead pads which are made from somecompositions within the range disclosed in U.S. Pat. No. 3,970,590 andcopper electronic leads soldered to the pads with a 50% lead, 50% indiumsolder have widely varying strengths with some being unacceptable weakboth initially and after being aged at elevated temperatures.

It is therefore an object of this invention to provide a solderable goldconductor composition that adheres to fired dielectric surfaces ofceramic substrates and to the surface of ceramic substrates withoutdielectric surfaces.

It is another object of this invention to provide an improved solderablegold conductor composition in which the conductor composition does notneed to be physically or chemically cleaned prior to soldering beyondthe action of noncorrosive fluxes compatible with the reliabilityrequirements of electronic systems such as digital computers.

It is still another object of this invention to produce an improvedsolderable gold conductor composition which optimizes the strength ofsolder bonds between leads of electronic components and the portions, orlead pads of the composition to which such leads are soldered whileretaining the characteristic that the pattern does not need to bephysically or chemically cleaned prior to soldering.

It is yet another object of this invention to provide an improved methodof soldering leads to lead pads on a substrate.

SUMMARY OF THE INVENTION

This invention relates to compositions of finely divided gold particlesand finely divided inorganic bonder particles dispersed in an inertliquid vehicle. The chemical composition of the binder and operative andpreferred proportions of the gold and binder are set forth in Table 1.The copper in the binder is present as compounds of copper, typicallyoxides, CuO, or Cu₂ O with the lead being present as PbF₂, and thecadmium as CdO. A composition of a glass suitable for use in the binderis disclosed in U.S. Pat. No. 3,970,590 which issued on July 20, 1976.It should be noted that this glass contains a substantial amount oflead, substantially 50% by weight of the glass and a small amount ofcadmium, substantially 2% by weight in addition to other ingredients.

                  TABLE I                                                         ______________________________________                                                    Proportions (wt %)                                                Component     Operative Preferred                                             ______________________________________                                        Gold          98-98.8   98.5                                                  Binder                                                                        Cu.sub.2 O    0.68-0.22 .56                                                   PbF.sub.2     0.35-0.24 .24                                                   CdO           0.34-0.23 .23                                                   Glass         0.6-0.5   .50                                                   ______________________________________                                    

In these compositions there are normally 7-15 parts vehicle andcomplementally, 85-93 parts inorganic solids (gold plus inorganicbinder), although these proportions may be varied depending upon thedesired printing properties of the composition.

The fired conductor patterns of this invention can be soldered withlead-indium solder to produce strong solder joints without it beingnecessary to preclean, either physically or chemically the firedconductors.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a graph of the relationship between the average peel strengthin pounds of solder joints between wire leads and solder pads ofconductor patterns using a 50% lead 50% indium solder as a function ofthe percent of copper by weight of the composition of the solder padswhen the joints have not been aged at an elevated temperature.

FIG. 2 is similar to FIG. 1 but shows the relationship between theaverage peel strength in pounds of such solder joints as a function ofthe percent of copper by weight of the composition of the solder padsafter the test samples are aged, or exposed, to a temperature of 75° C.for the periods of time indicated.

FIG. 3 is similar to FIG. 2 except that the solder joints were aged at atemperature of 100° C. for the times indicated prior to determining theaverage peel strength of the joints.

DETAILED DESCRIPTION OF THE INVENTION

Applicants have discovered that the amount of binder and particularlythe amount of copper in the form of its oxides, preferably Cu₂ O, in thebinder are critical in determining the solderability of the firedcomposition using a lead-indium solder while retaining good adhesion ofthe fired composition of a ceramic substrate such as one made fromcommercially pure, 96-97% alumina coated with a thin layer of a thickfilm dielectric of substantially 50 μm of alumina mixed with glass. Theamount of binder to produce such a solderable composition is in therange of 1% to 2% by weight based on solids. If the amount of copper inthe form of copper oxides in the binder is too low, the strength of thesolder bonds between electronic leads and lead pads made of thecomposition is too weak or small to produce an acceptable bond or joint,particularly after aging at temperatures to which it would be subjectedin electronic devices. However, if the amount of copper oxide is toohigh, the fired composition must be physically or chemically precleanedprior to solder which creates unacceptable process problems andreliability problems because of possible damage to electronic componentsmounted on substrates on which the composition is fired.

The inorganic particles used in the composition of this invention, noblemetal powders and inorganic binder powders, are usually described asfinely divided powders, and are generally sufficiently finely divided topass through a 200 mesh screen, preferably a 400 mesh screen (U.S.Standard Sieve Scale). Typically, substantially all the particles havedimensions in the range of 2 to 18 microns, preferably 2 to 14 microns.

The metal and binder particles are mixed with an inert liquid vehicle bymechanical mixing, e.g., in roll mills, to form a paste-likecomposition. The latter is printed as a thick film on conventionaldielectric substrates such as alumina or on such an alumina substratecoated with a thin layer substantially 50 μm of alumina mixed with glassin the conventional manner. Any inert liquid may be used as the vehiclesuch as water or any one of various organic liquids with or withoutthickening or stabilizing agents, or other common additives. Exemplaryof the organic liquids which can be used are terpenes, such as pine oil,terpineol and the like.

The ratio of inert liquid vehicle to solids in the dispersions may varyconsiderably and depends upon the manner in which the dispersion is tobe applied and the kind of vehicle used. While broad proportions ofsolids to vehicle can be used with the inorganic materials of thisinvention, preferred compositions comprise the proportions of noblemetal, binder, and vehicle set forth in the summary of the inventionabove. The compositions of the present invention may, of course, bemodified by the addition of other materials which do not affect theirbeneficial characteristics.

After drying to remove the inert vehicle, firing of the compositions ofthe present invention is carried out at temperatures and for timessufficient to sinter the inorganic materials and to produce conductorpatterns adherent to the dielectric substrate. Depending upon theproperties desired and composition used, preferred firing temperaturesare generally in the range of from 920°-930° C., preferably about 925°C., and the time at peak temperature is about ten minutes.

EXAMPLES

The following examples are presented to illustrate the invention. In theexamples and throughout the specification and claims all percentages,proportions, ratios, etc., are by weight unless otherwise specificallystated.

Compositions were made using 90.6 to 91.4 parts of inorganic solids(gold and binder) in 8.6 to 9.4 parts of a vehicle of a solvent based onterpineol with a thixotropic agent. The glass used in each example wasthe glass disclosed in U.S. Pat. No. 3,970,590.

In each sample of the material used (gold and binder) substantially allthe particles were equal to or greater than 2 microns and equal to orsmaller than 18 microns in diameter. In each example, binder, noblemetal, and vehicle were physically mixed and the resultant compositionwas printed through a 325 mesh screen (U.S. standard sieve scale) madefrom stainless steel wire 0.028 mm in diameter on a substrate made from96 to 97% alumina and having dimensions of 2 mm×80 mm×80 mm which iscoated with a layer of alumina mixed with glass in the range of from 50μm thick. The screen had 50 uniformly spaced openings 2.4 mm square withthe substrate surface being divided into 10 rectangles having dimensionsof 16 mm×40 mm. Five of the 2.4 mm square openings are aligned anduniformly spaced in each of said rectangles. The printed compositionswere allowed to level at a temperature in the range of from 110° to 130°C. for 15 minutes minimum in an air atmosphere. The dried compositionson the substrates were then fired in an air atmosphere in an oven, orfurnace, at a temperature of 925° C.±5° C. for seven minutes minimum.Rise and fall rates of the temperature were from 60° to 100° C. perminute. The total cycle time is 40 to 45 minutes. The fired thickness ofthe conductor lead pads was about 20±4 μm. The substrates are then sawedinto ten substantially equal test strips with 5 2.4 mm square lead padsof the pattern of fired composition on each strip. The lead pads on eachtest strip were not abraded, burnished or chemically cleaned except thateach test strip was degreased by being immersed in 1,1,1 trichloroethaneand then dried using nitrogen gas. Each test strip is then preheated ina Brown Bonder to a temperature of 135° C.±5° for three minutes. Eachconductor lead pad of a strip is then brushed with a pure water-whiterosin flux produced by Alpha Metals Inc. which is sold under the tradename 5002 Microflux, while the bonder is being cycled to +240°±5° C. Asolder preform of 50% indium, 50% lead is then placed on each of thefive lead pads on a test strip and allowed to flow for two seconds. Thetest strip is then allowed to cool for two minutes.

A tin coated 20 AWG copper lead wire is dipped into a solder potcontaining 50% indium, 50% lead solder at a +265°±5° C. with a layer of5002 flux on top of the solder. After the wire was coated with solder,it is dipped into perchloroethylene at +80°±5° C. to clean off the flux.The conductor lead pads with solder on them are then brushed with rosinflux. The test strip is then placed on a fixture and transferred to ahot plate where it is held at a temperature of 240°±5° C. When thesolder starts to reflow, the presoldered wire lead is placed in thecenter of a conductor lead pad. The test strip is left on the hot platefor substantially two minutes from the time the solder reflows and thenremoved. After the test strip has cooled, to solidify the solder, fluxis removed by dipping the test strip with wires soldered to theconductor lead pads in perchloroethylene at +80°±5° C.

The test strips with the solder wires is then left at room temperaturefor from 16 to 24 hours prior to "zero" hour adhesion measurements beingmade and prior to the beginning of thermal aging. The substrates whichare aged are stored in an oven at a temperature of 75°±2° C. or 100°±2°for various time periods.

To determine the peel strength of the solder bond between a wire leadand a lead pad of a conductor pattern to which it is soldered, the wirelead is bent so as to be perpendicular to the substrate, i.e., so thatthe center line of the portion of the wire perpendicular to thesubstrate is substantially 1.5 millimeters from the edge of the lead padto which it is soldered. The substrate with the test wires so bent isthen mounted on the test instrument, a Chatillon Model HTCM pull tester.A load is applied to a wire in a direction perpendicular to the bondplane at a point determined by the bonding radius, substantially 1/2inch per minute. As each lead pad is tested, a record is made of thestrengths recorded by the instrument at the time a failure occurs.Further, the failure mode is noted. If the wire separates from thesolder, the failure is denoted (WS). If the solder separates from thesolder pad, it is denoted (SP). If the wire, solder, and the conductorlead pad as an entity separates from the substrate, such a failure isdenoted (PD). Finally, if the conductor lead pad separates, or theconductor lead pad substantially splits in two along a plane parallel tothe top surface of the test strip, such a failure is denoted as (SPD)since it appears to be a combination of the SP and PD modes. The moredesirable types of failure are a ductile failure in the solder (WS orSP). The least desirable type of failure is a failure between a lead padand the substrates (PD).

A composition of the conductor material of a pattern was prepared havingthe components in the proportions set forth below.

                  TABLE II                                                        ______________________________________                                        Component     Proportion                                                      ______________________________________                                        Gold          98.98                                                           Cu.sub.2 O    .08                                                             CdO           .24                                                             PbF.sub.2     .26                                                             Glass         .44                                                             ______________________________________                                    

The results of pull tests on test strips were conducted as describedabove on the composition of Table II were as follows:

                  TABLE III                                                       ______________________________________                                                                 FORCE IN                                                                STD   POUNDS                                               TEMP      HRS     NMBR    AVG  DEV   LOW   HIGH                               ______________________________________                                        (1)   25       0      10    3.56 .32   3.1   4.0                              PD 10 3.6                                                                     (2)   100     48      10    2.96 .26   2.6   3.6                              PD 10 3.0                                                                     (3)   100     260     10    1.72 .38   1.2   2.3                              PD 10 1.7                                                                     ______________________________________                                    

In Table III Line (1) the 10 samples were held at room temperatures 25overnight which is denoted zero hours. The mean or average force atwhich the solder joints failed, their peel strength, is 3.56 lbs., thestandard deviation is 0.32 lbs., the weakest joint failed at 3.1 lbs.and the strongest at 4.0 lbs. In the line immediately below line (1) thetypes of failure and number of occasions of each type of failure arelisted plus the average force to the nearest tenth at which each suchtype of failure occurred.

EXAMPLE 2

A pattern of lead pads was printed, dried and fired on a substrate as inExample 1. The composition in this example had components in theproportion set forth in Table IV.

                  TABLE IV                                                        ______________________________________                                        Component     Proportion                                                      ______________________________________                                        Gold          98.91                                                           Cu.sub.2 O    .10                                                             PbF.sub.2     .27                                                             CdO           .26                                                             Glass         .46                                                             ______________________________________                                    

The results of pull tests on test strips conducted as described above onthe composition of Table IV were as follows:

                  TABLE V                                                         ______________________________________                                                               FORCE IN                                                                      POUNDS                                                 TEMP      HRS     NMBR    AVG  DEV   LOW   HIGH                               ______________________________________                                              25      0       50    6.01 1.14  4.5   9.1                              WS 1  8.6     PD48    5.9   CP1  6.8                                                75      48      15    5.77 .54   5.1   7.0                              PD 14 5.7     SPD1    6.2                                                           75      168     15    4.76 .84   3.3   6.1                              PD 15 4.8                                                                           75      336     15    5.33 .46   4.2   5.8                              PD 15 5.3                                                                           75      672     15    5.05 .53   3.8   5.6                              PD 14 5.0     SPD1    5.2                                                           75      1008    5     2.68 .57   2.2   3.6                              PD 5  2.7                                                                           75      1680    10    .00  .00   .0    .0                               PD 10 .0                                                                            100     48      15    5.23 .38   4.5   6.0                              PD 15 5.2                                                                           100     168     15    3.97 .39   3.4   4.8                              PD 15 4.0                                                                           100     336     15    .00  .00   .0    .0                               PD 15 .0                                                                            100     672     15    .00  .00   .0    .0                               PD 15 .0                                                                            100     1008    15    .00  .00   .0    .0                               PD 15 .0                                                                      ______________________________________                                    

EXAMPLE 3

The test strips were prepared as in Example 1 and the tests conducted asdescribed with respect to Example 1. The composition of the material ofthe conductor patterns had components in the proportions set forth inTable IV.

                  TABLE IV                                                        ______________________________________                                        Component     Proportion                                                      ______________________________________                                        Gold          98.84                                                           Cu.sub.2 O    .11                                                             CdO           .29                                                             PbF.sub.2     .28                                                             Glass         .48                                                             ______________________________________                                    

The results of pull tests on test strips conducted as described above onthe composition of Table IV were as follows:

                  TABLE VII                                                       ______________________________________                                                                 FORCE IN                                                                STD   POUNDS                                               TEMP      HRS     NMBR    AVG  DEV   LOW   HIGH                               ______________________________________                                              25      0       10    5.85 .36   5.4   6.4                              PD 10 5.8                                                                           75      240     10    5.28 .36   4.9   5.9                              PD 10 5.3                                                                     ______________________________________                                    

EXAMPLE 4

The test strips were prepared as in Example 1 and the tests conducted asdescribed with respect to Example 1. The composition of the material ofthe conductor patterns had components in the proportions set forth inTable VIII.

                  TABLE VIII                                                      ______________________________________                                        Component     Proportion                                                      ______________________________________                                        Gold          98.82                                                           Cu.sub.2 O    .15                                                             PbF.sub.2     .28                                                             CdO           .27                                                             Glass         .48                                                             ______________________________________                                    

The results of pull tests on test strips conducted as described above onthe composition of Table VIII were as follows:

                                      TABLE IX                                    __________________________________________________________________________                                FORCE IN                                                                  STD POUNDS                                            TEMP      HRS  NMBR                                                                              AVG  DEV LOW  HIGH                                         __________________________________________________________________________          25  0     50 718  .62 6.0  9.0                                          PD 11 6.9 CP27 7.1                                                                  75  48   15  6.93 .87 5.6  8.4                                          SPD 14                                                                              6.8                                                                           75  168  15  6.82 .30 6.2  7.3                                          CP 14 6.8                                                                           75  336  15  7.19 .63 6.4  9.0                                          SPD 14                                                                              7.2                                                                           75  672  15  7.86 .63 6.8  8.9                                          WS 3  8.3 SP7  7.7 SPD5 7.8                                                         75  1008  5  6.28 1.10                                                                              4.5  7.1                                          SPD 5 6.3                                                                           75  1680 10  1.22 1.09                                                                              .0   2.7                                          PD 10 1.2                                                                           100 48   15  6.12 .55 5.3  7.2                                          PD 2  5.6 SPD13                                                                              6.2                                                                  100 168  15  5.41 .75 4.0  6.2                                          CD 12 5.2                                                                           100 336  15  2.69 .78 1.7  4.1                                          PD 11 2.4 SPD4 3.5                                                                  100 672  15   .11 .44 .0   1.7                                          PD 15 .1                                                                            100 1008 15   .00 .00 .0   .0                                           PD 15 .0                                                                      __________________________________________________________________________

EXAMPLE 5

The test strips were prepared as in Example 1 and the tests conducted asdescribed with respect to Example 1. The composition of the material ofthe conductor patterns had components in the proportions set forth inTable X.

                  TABLE X                                                         ______________________________________                                        Component     Proportion                                                      ______________________________________                                        Gold          98.91                                                           Cu.sub.2 O    .22                                                             PBF.sub.2     .24                                                             CdO           .23                                                             Glass         .40                                                             ______________________________________                                    

The results of pull tests on test strips conducted as described above onthe composition of Table X were as follows:

                  TABLE XI                                                        ______________________________________                                                                 FORCE IN                                                                STD   POUNDS                                               TEMP      HRS    NMBR    AVG   DEV   LOW   HIGH                               ______________________________________                                              25      0      35    7.27  .90   5.8   9.9                              WS 6  8.5     SP1    9.0   PD9   6.4   SPD19 7.2                                    100     48     15    5.54  .91   4.6   8.0                              PD 13 5.3     CP2    7.1                                                            100     168    15    5.25  .66   4.3   6.8                              PD 19 5.5     CP5    4.8                                                            100     336    15     .43  .60    .0   1.8                              PD 15 .4                                                                            100     672    15     .00  .00    .0   .0                               PD 15 0                                                                             100     1008   15     .00  .00    .0   .0                               PD 15 .0                                                                      ______________________________________                                    

EXAMPLE 6

The test strips were prepared as in Example 1 and the tests conducted asdescribed with respect to Example 1. The composition of the material ofthe conductor patterns had components in the proportions set forth inTable XII.

                  TABLE XII                                                       ______________________________________                                        Component     Proportion                                                      ______________________________________                                        Gold          98.75                                                           Cu.sub.2 O    .34                                                             PbF.sub.2     .25                                                             CdO           .24                                                             Glass         .42                                                             ______________________________________                                    

The results of pull tests on test strips conducted as described above onthe composition of Table XII were as follows:

                                      TABLE XIII                                  __________________________________________________________________________                                  FORCE IN                                                                 STD  POUNDS                                          TEMP      HRS  NMBR AVG  DEV  LOW  HIGH                                       __________________________________________________________________________         25   0    50   7.63 .52  7.6  9.0                                        WS 2 8.8  PD1  7.6  CP5  8.0                                                       75   48   15   7.77 .67  8.3  8.9                                        WS 1 8.9  CP1  8.3                                                                 75   168  15   7.49 .59  7.0  8.5                                        CP 9 7.8                                                                           75   336  15   8.18 .77  8.8  9.5                                        SPD 3                                                                              9.1                                                                           75   672  15   7.60 .78  6.8  9.4                                        WS 2 8.8  SP13 7.4                                                                 75   1008  5   4.55 .65  3.7  5.5                                        SPD 5                                                                              4.5                                                                           75   1680 10   2.85 .37  2.3  3.5                                        PD 10                                                                              2.9                                                                           100  48   15   7.44 .67  6.0  8.4                                        CP 4 7.7                                                                           100  168  15   6.90 .58  .0   .0                                              100  336  15   3.61 .59  2.8  4.8                                        PD 6 3.3  SPD9 3.3                                                                 100  672  15    .00 .00  .0   .0                                         PD 15                                                                              .0                                                                            100  1008 15    .00 .00  .0   .0                                         PD 15                                                                              .0                                                                       __________________________________________________________________________

EXAMPLE 7

The test strips were prepared as in Example 1 and the tests conducted asdescribed with respect to Example 1. The composition of the material ofthe conductor patterns had components in the proportions set forth inTable XIV.

                  TABLE XIV                                                       ______________________________________                                        Component     Proportion                                                      ______________________________________                                        Gold          98.4                                                            Cu.sub.2 O    .61                                                             CdO           .25                                                             PbF.sub.2     .26                                                             Glass         .48                                                             ______________________________________                                    

The results of pull tests on test strips conducted as described above onthe composition of Table XIV were as follows:

                                      TABLE XV                                    __________________________________________________________________________                                  FORCE IN                                                                 STD  POUNDS                                          TEMP      HRS  NMBR AVG  DEV  LOW  HIGH                                       __________________________________________________________________________         75   168  14   7.83 1.22 5.6  9.4                                        SP 8 7.7  PD1  7.2  SPD1 7.3  CP4  8.5                                             75   336  14   7.52 1.32 5.9  9.8                                        WS 3 9.3  SP8  7.1  SPD1 6.5  CP2  7.2                                             75   672  14   7.39 1.30 5.8  9.9                                        WS 3 9.3  SP8  6.4  CP3  8.1                                                       75   1008 14   7.23 1.19 5.9  9.8                                        WS 5 8.5  SP9  6.5                                                                 100  336  14   5.20 1.36 3.7  8.2                                        WS 1 7.6  SP11 4.8  CP2  6.1                                                       100  672  14   4.23 .69  3.2  5.5                                        SP 5 4.7  SPD9 3.9                                                                 100  1008 14   1.99 .51  1.4  3.2                                        PD 14                                                                              2.0                                                                      __________________________________________________________________________

EXAMPLE 8

The test strips were prepared as in Example 1 and the tests conducted asdescribed with respect to Example 1. The composition of the material ofthe conductor patterns had components in the proportions set forth inTable XVI.

                  TABLE XVI                                                       ______________________________________                                        Component     Proportion                                                      ______________________________________                                        Gold          97.64                                                           Cu.sub.2 O    1.31                                                            CdO           .25                                                             PbF.sub.2     .26                                                             Glass         .54                                                             ______________________________________                                    

It should be noted that test strips having the composition of Table XVcould not be soldered until after they had been abraded physically orchemically cleaned. After being appropriately cleaned, leads weresoldered to the pads of the strips. The results of pull tests on suchtest strips after being cleaned and then soldered were as follows:

                                      TABLE XVII                                  __________________________________________________________________________                                FORCE IN                                                                  STD POUNDS                                            TEMP      HTS  NMBR                                                                              AVG  DEV LOW  HIGH                                         __________________________________________________________________________          100 168  15  7.20 1.07                                                                              5.1  9.4                                          WS 7  7.9 SP6  6.4 CP2  7.1                                                         100 336  15  6.30 .98 4.2  7.4                                          WS 6  7.0 SP7  5.7 CP2  6.5                                                         100 672  15  5.15 1.05                                                                              3.9  7.7                                          WS 1  7.7 SP13 4.8 CP1  6.9                                                   100   1008                                                                               14   4.64                                                                              .62 3.3 5.5                                               SPD 14                                                                              4.6                                                                     __________________________________________________________________________

The data of Tables III, V, VII, IX, XI, XIII, XV and XVII which providethe average peel strength in pounds at which the solder joints failedprovide the points used in determining the curves of FIGS. 1, 2 and 3.Peel strength is the ordinate and the percent of copper is the abscissa.A perusal of FIG. 1 which is a plot of the points for no aging, or moreaccurately where the test samples were stored at room temperature for upto a maximum of 24 hours, shows a very rapid drop off in the strength ofsuch joints beginning at around 0.2% copper as the amount of copper isdecreased with a substantial leveling off of the peel strength of suchjoints as the amount of copper is increased at least through 1.1% Cu.

In FIGS. 1, 2 and 3, for purposes of illustration, the units of theabscissa are expressed in weight percentage of copper which is derivedfrom the weight percentage of Cu₂ O by multiplying the weight percentageof Cu₂ O by the ratio of the atomic weight of 2 Cu by the atomic weightof Cu₂ O: ##EQU1##

The data used in FIG. 2 was obtained from test strips which were aged at75° C. a temperature which approximates the upper end of thetemperatures to which the joints would be subjected in electronicsystems such as computers. There is a band of closely spaced pointsbetween tests after 48 hours and 1,008 hours in which the pad strengthof the solder joints does not decrease very rapidly as a function oftime. Thereafter there is a rapid fall off in the peel strength between1,000 hours and 1,680 hours. Again the curves drop off very rapidly whenthe amount of copper is reduced below 0.2% copper.

In FIG. 3, the data was obtained from test strips which were aged at100° C. The cruves show a decrease in peel strength as a fraction ofaging time. Again there is a rapid drop off in peel strength as theamount of copper in the composition is decreased below 0.2% but anincrease in the strength of the joints after aging as the amount ofcopper is increased. The test results indicate that increasing theamount of copper tends to increase the strength of the jointsparticularly after aging.

However, somewhere in the range of from 0.54 and 1.1% of copper thecomposition can no longer be soldered without some form of chemical orphysical cleaning of the pattern after it has been sintered on thesubstrate. Thus, Applicants have discovered that there is an optimumrange in the amount of copper in the composition between 0.2% and 0.6%at which the pattern is solderable without having to be cleaned andproduces solder joints of acceptable strength. It should be noted thatthe peel strength of the joints decreases more slowly as a function ofaging as the amount of copper is increased until a maximum amount ofcopper is present. However, beyond a maximum amount of Cu the firedcomposition must be cleaned immediately prior to soldering if goodsolder joints are to be obtained, which is an unacceptable condition. Inall such tests the adhesion of the fired composition to the substrateafter firing was good.

In general the peel strengths of the samples having less than 0.2%copper have a relatively rapid rate of degradation as a function of timeand temperature with the lower limit of the amount of copper that willproduce joints of acceptable strength being about 0.2% . In the range offrom 0.2 to 0.6% copper the strength of such joints both initially andafter aging has more stability for longer periods of time under eachthermal condition. While the 1.0% copper composition exhibited excellentinitial characteristics and aging characteristics, it does not have thedesirable attribute of being solderable without being prepared either byphysical abrasion or by a chemical cleaning. The lower limit of thedesired range of the copper is 0.2% and the upper limit is substantially0.6%.

What is claimed is:
 1. A conductor composition comprising:finely dividedgold particles and finely divided inorganic binder particles dispersedin an inert liquid vehicle having by weight 98.2 to 98.7 gold particlesand, complementally, 1.8 to 1.3% inorganic binder particles, the binderconsisting essentially of by total weight of gold and binder, 0.35 to0.24 percent PbF₂, 0.34 to 0.23 percent CdO, 0.68 to 0.39 percent Cu₂ O,and the balance glass.
 2. The method of soldering a lead to a lead padon a substrate comprising the steps of: printing a conductor patternincluding at least one lead pad on the substrate using a goldcomposition, said gold composition being composed of finely divided goldparticles and finely divided inorganic binder particles dispersed in aninert liquid vehicle, by weight 98.2 to 98.7% gold particles andcomplementally 1.8 to 1.3% inorganic binder particles, the binderconsisting essentially by total weight of gold and binder of:0.68 to0.39 percent Cu₂ O 0.35 to 0.24 percent PbF₂ l 0.34 to 0.23 percent CdOand the balance glass: allowing the print to level at room temperature:heating the substrate to a temperature substantially not exceeding 130°C. until substantially dry; firing the substrate to sinter the inorganicmaterials; vapor degreasing the fired substrate; applying a solder fluxto the lead pad; placing a solder preform on the lead pad; heating thesubstrate to allow the solder on the lead pad to liquify: cooling thesubstrate to solidify the solder; presoldering a lead; cleaning flux offof the lead; applying solder flux to the solder on the lead pad; heatingthe substrate to a temperature at which the solder begins to reflow:placing the presoldered wire on the lead pad; maintaining the solder ina liquid state for a predetermined period of time: cooling the substrateto ambient temperature, and cleaning the substrate and the lead solderedto the lead pad.
 3. The method of soldering a copper lead to a lead padon an alumina substrate having a thin dielectric layer of alumina fixedwith glass on one surface of the substrate comprising the steps of:printing a conductor pattern including a lead pad on the dielectriclayer of the substrate using a gold composition, said gold compositionbeing composed of finely divided gold particles and finely dividedinorganic binder particles dispersed in an inert liquid vehicle, byweight 98.5% gold particles and complementally 1.5% inorganic binderparticles, the binder consisting essentially by total weight of gold andbinder of:0.56 percent Cu₂ O 0.24 percent PbF₂ 0.23 percent CdO, and thebalance glass; allowing the print to level at room temperature, dryingthe print for twenty minutes in air at a temperature of from 110° to130° C.; firing the substrate at a temperature of 125°±5° for sevenminutes minimum, the rise and fall rate being from 60° to 100° C. perminute, the total cycle time being of the order of 40-45 minutes in air;vapor degreasing the fired substrate with trichloroethane; drying thesubstrate with nitrogen gas; placing the substrate in a preheat stageand raising the temperature to 135° C.±5° for three minutes; applying anon-activated liquid rosin solder flux to the lead pad at a temperatureof about 240° C.±5° C.; placing a solder preform 50% indium, 50% lead onthe lead pad; allowing the solder to flow for two seconds; cooling thesubstrate for approximately two minutes; presoldering a copper lead with50% indium, 50% lead; dipping the presoldered lead into puretrichloroethylene at plus 80°±5° to clean off the flux; applying anon-activated liquid rosin solder flux to the solder on the lead pad;heating the substrate to a temperature at which the solder on the leadpad begins to reflow; placing the presoldered wire in the liquid solderon the lead pad; continuing to heat the substrate to maintain the solderin a liquid state for approximately two minutes; and cooling thesubstrate, the lead pad and the lead; and cleaning the substrate andlead soldered to the lead pad with trichloroethylene at plus 80°±5° C.